The long range goal is to understand the mechanisms that regulate the biosynthesis of phosphatidylcholine and the 1,2 - dipalmitoyl species in the lung and during lung development. The dipalmitoyl species of phosphatidylcholine is an important component of pulmonary surfactant, a substance necessary for lung function. Since the control of phosphatidylcholine biosynthesis is relatively unknown in any tissue, a comprehensive investigation of the basic regulatory mechanisms is fundamental to studies on the control during lung development. The research in this proposal is guided by the hypothesis that the biosynthesis of phosphatidylcholine is regulated by the supply of both diacylglycerol and CDP choline which in turn are coordinated by the reversible formation of a multienzyme complex on the endoplasmic reticulum. This complex would contain cytidylyltranserase, phosphatidate phosphohydrolase and choline-phosphotransferase. The present studies focus on the cytidylyltransferase component and will 1) provide detailed information about the molecular properties and subcelluar forms of cytidylyltransferase, 2) define the biochemistry of the translocation of cytidylyltransferase to membrane binding sites 3) characterize the binding domains on the membrane and 4) explore the possible existence of a multienzyme complex formed as a result of the translocation. Antibodies for cytidylyltranserase will be used to locate subcellular forms, to develope immunoassay for cytidylyltranserase and to isolate native forms of the enzyme. The mechanism which modulate translocation will be studied using in vitro systems and hepatocytes and HeLa cells in culture. An important part of these studies is to determine whether cytosolic or membrane components function in the regulation of the activity and subcellular location of cytidylyltransferase.